Abstract: A posture improving waist expansion monitoring device which includes a housing which contains an alarm and sensing mechanism, a one-piece belt fastened at one end of the housing and attached to one of the legs of a four-sided round-wire ring at the other end via a flat hook, the length of the belt being adjustable by means of a slide ring. When the wearer's waist is in a contracted position, there is no alarm since the circuit is not completed; however when the waist is expanded and the belt has been preadjusted such that in this enlarged condition the leaf spring completes the electric circuit and consequently actuating the alarm in the housing.